Do you suggest treating the whole tank, or just the sick guy?Treat with API General Cure. Then proceed to use the epsom salt solution on floating pellets/gel food/dehydrated krill until over saturated.
Yep... the albino oscar was definitely being picked on. I could see it, as well as evidence later, with the nipped fins. The regular oscar, however, HE would sometimes chase bully the jack a bit. Not enough to cause any damage, but only to show him who the boss with. I have no doubt that, for now, the oscar was the boss. The jack would watch himself with the regular oscar, but not the albino.Being picked on by other fish can be enough stress to cause immune suppression so the normally benign bacteria in the gut becomes infectious (and those bacteria are always present waiting for an opportunity to flourish).
Compared to many other cichlids, especially if those are more already intrenched, oscars are on the mild side, and can be easily stressed to death, by more dominant types (the JD may be the culprit), and especially in a tank as small as a 75 where there isn't enough escape space.
JDs (and most cichlids) usually don't break off chase until they hit 4 ft, .
Either way, gotta solve the problem now. Hopefully, it doesn't get any worse.